Turbine blade for an aircraft engine and casting mold for its manufacture

ABSTRACT

A hollow-type turbine blade produced by a casting process has a cooling air cavity ( 8 ) and film cooling ducts ( 12 ) originating at this cooling air cavity ( 8 ). Adjacent film cooling ducts with a large length-diameter ratio are connected by cross-ducts ( 13 ) which are offset relative to each other and arranged vertically to the film cooling ducts. The casting mold comprises a core corresponding to a brickwall design of the film cooling ducts and the cross-ducts, with long core pins being intersupported by cross pins. The turbine blade, including all film cooling ducts, can be produced with high quality in a casting process.

This application claims priority to German Patent ApplicationDE10346366.6 filed Sep. 29, 2003, the entirety of which is incorporatedby reference herein.

BACKGROUND OF THE INVENTION

This invention relates to a turbine blade made in a casting process withat least one radial cavity flown by cooling air and a multitude of filmcooling ducts, radially spaced and arranged one above the other,extending from the inner surface of the cavity to the outer surface and,further, this invention relates to a casting mold for the manufacture ofthe turbine blade in a casting process using a soluble core for theproduction of the cavities.

One primary goal in the effort to enhance the performance of aircraftgas turbine engines is the increase of the temperature of the turbinegases. Internal cooling of the turbine blades counteracts theconstraints set in this respect by the limited heat resistance of theavailable materials. The cooling air, upon entering central, radialcavities in the interior of the blades, is routed to the outside via amultitude of minute film cooling ducts arranged radially spaced from theairfoil bottom to the blade tip to produce a cooling air film on theouter surface of the blade. This cooling air film forms a barrier layerbetween the surface of the turbine blade and the hot gases impingingonto the blade surface to cool, in particular, the blade pressure sideand here, especially, the turbine blade trailing edge which, due to itssmall thickness, is sensitive to stresses and problematic with regard tocooling. Turbine blades with a multitude of film cooling ducts in thearea of the trailing edge which, due to the small material thickness inthis blade area, are long and thin and which are arranged parallellyspaced relative to each other are known from Patent Specifications EP 0916 809 A2 or DE 40 03 804 C2, for example.

The manufacture of turbine blades with film cooling ducts in the area ofthe blade trailing edge is, however, difficult in that these ducts, uponforming the blades, are to be produced by a demanding machining methodon the basis of electric discharge processes, namely electro-dischargemachining (EDM), and in that this method is costly and incurs thehighest scrap rate in the entire manufacturing process.

Currently, the casting of turbine blades together with the film coolingholes at the trailing edge is not possible or, the modern castingprocesses, for example on the basis of virtual pattern casting or thecasting method with water-soluble core, in which the core residues inthe inner of the finished casting are dissolved out with suitable means,are disadvantageous in that the respective core sections (thin pins) forthe long, thin trailing-edge film cooling ducts do not withstand thehigh stresses occurring in the casting mold making process (baking). Invirtual pattern casting (VPC), the core sections are ceramic pins thatare liable to break during the making of the casting mold or inconsequence of the stresses occurring when the metal cools in the mold.If the thin ceramic pins forming certain portions of the mold breakbefore the casting process is fully finished, the film cooling ductswill not be formed completely, i.e. they will be fully or partlyblocked, thus rendering the blade unserviceable.

BRIEF SUMMARY OF THE INVENTION

The present invention, in a broad aspect, provides a casting mold and aturbine blade for gas turbine engines produced by means of this mold,enabling the blade to be cost-effectively manufactured in a castingprocess, while ensuring high quality and adequate cooling.

It is a particular object of the present invention to provide a solutionto the above problems by a casting mold and a corresponding turbineblade designed in accordance with the features described herein. Certainfeatures of the present invention will be apparent from the descriptionbelow.

The concept underlying the present invention is to produce the turbineblade in its entirety, i.e. including the area of the trailing-edge filmcooling ducts with a large length-diameter ratio, by means of a castingmold using a core soluble upon performance of the casting process, withvery long, thin core pins being, however, intersupported by cross-pins.Thus, the stresses occurring during baking and cooling of the core andduring and after the casting process will not damage the long core pins,allowing the turbine blade, including the film cooling ducts, to becost-effectively produced in a casting process.

The turbine blade according to the present invention featurescross-ducts between the film cooling ducts which correspond to thecross-pins and which extend vertically to the film cooling ducts. Thisarrangement of the cross ducts relative to the film cooling ductsensures that the cooling air will only flow in the direction of the filmcooling ducts, i.e. will not be diverted, thus providing the requiredcooling air film and the required cooling effect.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is more fully described in the light of theaccompanying drawings, showing a preferred embodiment. In the drawings,

FIG. 1 is a sectional view of a hollow, cast turbine blade with filmcooling ducts provided in the outer wall on the pressure side, and

FIG. 2 is a sectional view along line AA in FIG. 1 showing the long filmcooling ducts provided in the area of the trailing edge of the turbineblade.

DETAILED DESCRIPTION OF THE INVENTION

The hollow-type turbine blade 1 produced by a precision casting processwith a lost core (soluble upon performance of the casting process) has apressure side 2, a suction side 3, a leading edge 4 and a trailing edge5. Partitions 6 between the outer walls 7 of the turbine blade 1 definecooling air cavities 8 extending in the radial direction of the turbineblade which provide the blade interior with cooling air supplied viaopenings in the blade root (not shown). The cooling air enters adjacentcavities 10 in the blade interior via cooling ducts 9 in the partitions6 and/or flows to the outside via film cooling ducts 11 or 12,respectively, radially spaced in the outer wall 7. The air exiting fromthe film cooling ducts 11 or 12, respectively, produces a cooling gasfilm flowing along the outer wall to cool, in particular, the pressureside 2 of the turbine blade 1.

The film cooling ducts 12 at the trailing edge 5 of the turbine blade 1are connected to each other by at least one cross-duct 13 in the area inwhich the film cooling ducts 12 exceed a certain length, i.e. in thearea where their length-diameter ratio is particularly large. Thecross-ducts 13 which lie adjacent to each other in the radial(longitudinal) direction of the turbine blade 1 are offset relative toeach other in brickwall style and are positioned at angles to the filmcooling ducts 12, and in the embodiment shown, generally normal to thefilm cooling ducts 12. This generally normal arrangement of thecross-ducts 13 relative to the film cooling ducts 12 ensures that thecooling air will pass through the film cooling ducts 12 completely andactually reach the required cooling areas at the trailing edge 5 of theturbine blade 1.

The brickwall design of the film cooling ducts with largelength-diameter ratio is created by the special core structure of thecasting mold (not shown) for the production of the turbine blade 1,namely in the area of the trailing edge 5. There, the long, thin corematerial (core pins) for the production of the film cooling ducts 12,which is arranged radially spaced and parallel above one another, issupported by cross-pins which are radially offset relative to each otherand arranged generally normal to said core material. The representationof the core structure has been dispensed with in the present embodimentsince it corresponds exactly with the brickwall design of the filmcooling ducts connected by the cross-ducts shown in FIG. 2. This corestructure for the production of the trailing edge 5 prevents the thincore material provided for the formation of the long film cooling ducts12 from breaking due to shrinkage stresses resulting from the cooling ofthe baked casting mold and the core or due to stresses resulting fromthe cooling of the hot metal melt injected into the casting mold, thusproviding for complete formation of the film cooling ducts 12 uponremoval or evacuation of the core material from the casting, i.e. theturbine blade 1, according to the lost mold principle and ensuringefficient film cooling at the trailing edge 5 of the turbine blade 1.

This core for the casting mold and the resultant form of the turbineblade in the area of the film cooling ducts 12 at the trailing edge 5provides for cost-effective, high-quality production of the turbineblades, including the film cooling ducts, by means of a casting process.

LIST OF REFERENCE NUMERALS

-   1 Turbine blade-   2 Pressure side-   3 Suction side-   4 Leading edge-   5 Trailing edge-   6 Partition-   7 Outer wall-   8 Cooling air cavity-   9 Cooling ducts of partition 6-   10 Cavities-   11 Film cooling ducts of outer wall 7-   12 Film cooling ducts at trailing edge-   13 Cross-duct

1. A casting mold for the production of a hollow turbine blade having atleast one radial cavity flown by cooling air and a multitude of filmcooling ducts, radially spaced and arranged one above the other,extending from an inner surface of the cavity to an outer surface, themold comprising an investment surrounding a core for the production ofcavities and ducts which is soluble upon casting, wherein, the core forthe formation of film cooling ducts having a large length-diameter ratiocomprises a multitude of core pins of an extension corresponding to theduct length which, in a longitudinal direction of the casting mold, arespaced and arranged one above the other and in that adjacent core pinsare connected to each other by at least one cross-pin which is arrangedgenerally normal to the core pins and which intersupports the core pinsduring a core making and a casting process.
 2. A casting mold inaccordance with claim 1, wherein, in the longitudinal direction of thecasting mold, adjacent cross-pins, that lie above one another, arearranged regularly offset to each other.
 3. A casting mold in accordancewith claim 2, wherein a number of cross-pins arranged between two corepins is variable in dependence of the length of the core pins.
 4. Acasting mold in accordance with claim 3, wherein the cross-pins arerelated to the core pins in an area of a portion of the mold forming thetrailing edge of the turbine blade.
 5. A casting mold in accordance withclaim 1, wherein the cross-pins are related to the core pins in an areaof a portion of the mold forming the trailing edge of the turbine blade.6. A casting mold in accordance with claim 1, wherein a number ofcross-pins arranged between two core pins is variable in dependence ofthe length of the core pins.
 7. A cast turbine blade for an aircraftengine having a leading edge, a trailing edge and at least one internalradial cooling air-supplied cavity from which a plurality of cast,radially spaced film cooling ducts extend to an outer surface of theblade to produce a cooling air film, the turbine blade furthercomprising a plurality of cast cross-ducts, each cross-ductinterconnecting two adjacent film cooling ducts, the cross-ducts beingpositioned generally normal to the film cooling ducts with adjacentcross-ducts connected to a film cooling duct being offset from oneanother.
 8. A turbine blade in accordance with claim 7, wherein a numberof the cross-ducts between adjacent film cooling ducts is set independence of a length of the film cooling ducts.
 9. A turbine blade inaccordance with claim 8, wherein adjacent cross-ducts connected to afilm cooling duct are offset from one another along a length of the filmcooling duct.
 10. A turbine blade in accordance with claim 9, whereinthe cross-ducts are related to the film cooling ducts in an area of thetrailing edge of the turbine blade.
 11. A turbine blade in accordancewith claim 7, wherein adjacent cross-ducts connected to a film coolingduct are offset from one another along a length of the film coolingduct.
 12. A turbine blade in accordance with claim 7, wherein thecross-ducts are related to the film cooling ducts in an area of thetrailing edge of the turbine blade.
 13. A method of producing coolingducts in a turbine blade for an aircraft engine, the turbine bladehaving a leading edge, a trailing edge and at least one radial coolingair-supplied cavity, the cooling ducts being radially spaced andextending from the air-supplied cavity to an outer surface of the bladeto produce a cooling air film, comprising: producing a lost core castingmold for precision casting the turbine blade, forming a core portionfrom a material soluble upon casting of the turbine blade, the coreportion having a plurality of core pins of an extension corresponding todesired lengths of the cooling ducts which, in a longitudinal directionof the casting mold, are spaced and arranged one above the other, thecore pins forming the cooling ducts in the turbine blade when the corematerial is dissolved during casting of the turbine blade; forming aplurality of core cross-pins, each of the core cross-pinsinterconnecting at least two of the core pins to support the connectedcore pins until dissolved during the casting of the turbine blade, thecore cross-pins being formed generally normal to the core pins, the corecross-pins forming cross-ducts between the interconnected cooling ductswhen the core is dissolved during the casting of the turbine blade; andcasting the turbine blade to remove the core portion and form theturbine blade.
 14. A method in accordance with claim 13, wherein thenumber of core cross-pins formed between adjacent core pins is varied independence of the length of the core pins.
 15. A method in accordancewith claim 14, wherein adjacent core cross-pins connected to a core pinare offset from one another along a length of the core pin.
 16. A methodin accordance with claim 15, wherein the cooling ducts are formed in anarea of the trailing edge of the turbine blade.
 17. A method inaccordance with claim 13, wherein adjacent core cross-pins connected toa core pin are offset from one another along a length of the core pin.18. A method in accordance with claim 13, wherein the cooling ducts areformed in an area of the trailing edge of the turbine blade.